Fstab (file system table) is a configuration file that is used to define howdisk partition, file system, and file share mounts in your Linux VM persistacross system reboots.

This document outlines multiple conditions where an incorrect fstabconfiguration may result in a boot problem and offers troubleshootingadvice to fix the issue.

A few of the common issues with fstab misconfiguration are listed below:

• Syntax error infstab configuration file
• An incorrect UUID
• An entry exists for an unattached/unavailable device
• Deprecated mount options likenobarrier for the xfs file systemtype inSUSE orRHEL images.

Before you begin

• If you want to log serial port output in Cloud Logging, familiarize yourself withCloud Logging.
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  gcloud

  1. Install the Google Cloud CLI. After installation,initialize the Google Cloud CLI by running the following command:

     gcloudinit

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     Note: If you installed the gcloud CLI previously, make sure you have the latest version by runninggcloud components update.
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  REST

  To use the REST API samples on this page in a local development environment, you use the credentials you provide to the gcloud CLI.

  Install the Google Cloud CLI. After installation,initialize the Google Cloud CLI by running the following command:

  gcloudinit

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  Note: If you installed the gcloud CLI previously, make sure you have the latest version by runninggcloud components update.

  For more information, seeAuthenticate for using REST in the Google Cloud authentication documentation.

Identify fstab issues

For boot issues, Google highly recommendeds that you check the boot logsin the Serial Console of the Linux VM. The VM goes into emergency modewith an error message hinting that the issue is with fstab.

  [K[[1;31m TIME [0m] Timed out waiting for device dev-incorrect.device.  [[1;33mDEPEND[0m] Dependency failed for /distribution.  [[1;33mDEPEND[0m] Dependency failed for Local File Systems.  ...  Welcome to emergency mode! After logging in, type "journalctl -xb" to viewsystem logs, "systemctl reboot" to reboot, "systemctl default" to try again to boot into default mode.  Give root password for maintenance  (or type Control-D to continue)

As per the error message, there is dependency failure for the/distributionfile system. The dependency failure for a file system mount point will differbased on the file system names used.

Resolution

Use the following options to solve thefstab error in Linux VMs hostedin Google Cloud. You can resolve the issue faster using the serial consolethan using the manual method.

To use the following methods to resolve the fstab issue, you mustenable serial port access for your VM.

Option 1: Use the serial console to log into the VM in emergency mode

1. Log into the serial console of the VM from Google Cloud console.

2. In the current emergency mode, enter the root password to access your VM.

3. Use your favorite text editor to open thefstab file. Make thenecessary changes and save the changes to thefstab file. In thefollowing example, thevi editor is used.

   vi /etc/fstab

   

   In the previous example, the device for/distribution is detached fromthe VM. Comment the line that references the file system or remove thefstab entry for/distribution mount point.

   Useman fstab for moredetails about the fstab configuration and syntax.

4. Save the file and exit the editor. If you are using thevi editor, useESC +:wq! to save and exit the editor.

5. Resume the boot process by enteringreboot at the prompt.

6. After successfully fixing the issue, the VM boot process should completeand the login prompt appears in the serial console.

7. Verify you can log in to the VM again using SSH.

Option 2 - Using Single User mode in Serial Console

This option can be used if the root password is not set.

Prerequisite: TheGRUB_TIMEOUT parameter in the grub configuration filemust be set to a non-zero value. Usually this file is at/etc/default/grub, but on some earlier distributions, it might be locatedin a non-standard directory.

1. Go to the VM instances page in the Google Cloud console.Go to VM instances

2. Log into the serial console of the Virtual Machine from theGoogle Cloud console.

3. ClickRESET for virtual machine from Google Cloud Console.

   

4. In the serial console window, interrupt the boot process by clicking thearrow key to pause in the grub screen or menu.

5. In the list of kernels in the grub boot loader screen, choose the kerneland presse on the keyboard.

   

6. Add therd.break parameter at the end of the kernel line and pressctrl+x. This helps in booting the VM into single user mode.

   

   Note: Therd.break parameter works for RHEL, CENTOS, Oracle Linux,SUSE Operating Systems. This parameter isn't a persistent entryso no changes are required after boot. For Ubuntu 18.04, 20.04and 22.04 LTS, you can addsystemd.unit=rescue.target to boot intorescue mode which is similar to single user mode.

7. Mount the root file system in read write mode.

8. Analyze, make necessary change and savefstab file. Useman fstab for moredetails about configuration and syntax. Use your favorite text editor toopen thefstab file. In the below example, the vi editor is used.

   vi /etc/fstab

   

   In this example, the device for/distribution is detached from the VM,so comment the line or remove the fstab entry for the/distributionmount point.

9. Save the file and exit from the editor. If you are using the vi editor, then useESC +:wq! to save and exit from fstab.

10. Resume the boot process by enteringreboot at the prompt.

11. After successfully fixing the issue, the VM boot process should complete andyou should see the login prompt in the serial console.

12. Verify you can log in to the VM using SSH.

Option 3 - Rescue the VM

This option can be used if the root password is not set or if you can't usesingle user mode.

For more information, seeRescue an inaccessible VM.